Thermal relay for electric discharge lamp



March 23, 1943. H. J. MCCARTHY 2,314,725

y THERMAL RELAY FOR ELECTRIC DISCHARGE LAMP-S v H871 Ty]. McCa Tthy, INVENTOR.

ATTO BNEY March 23, 1943., H. J. MCCARTHY 2,314,725

THERMAL RELAY FOR ELECTRIC DISCHARGE LAMPS Filed Dec. 28; 1940 2 Sheets-Sheet 2 HQTUyJMCCdTtImINVENTOR.

BYM M ATTOENEY Patented Mar. 23, 1943 THERMAL RELAY FOR ELECTRIC DISCHARGE LALIP Henry J. McCarthy, Danvers, Mass., assignor to Sylvania Electric Products, a

Massachusetts corporation of Application December 28, 1940, Serial No. 372,154

g 1 Claim.

This invention relates to auxiliary apparatus for electric gaseous discharge lamps and more particularly to a thermal relay therefor.

An object of this invention is to obtain a relay that will provide a distinctly positive contact, especially in restarting when a lamp has failed to light the first time."

' Another object is to provide a relay that will not go off and on intermittently after a lamp has failed to start the first time. I

Further objects, advantages and features will be apparent from th specification below, taken in conjunction with the accompanying drawings in which:

Figure Us a front elevation showing the thermal relay as it appears when it is not operating.

' Figure 2 is a front elevation. showing thev thermal relay as it appears when the lamp is actually running.

Figure 3 is a detail of the bimetallic strips when th relay is not operating.

Figure 4 is a side elevation of the bimetallic strips when the relay is not operating.

Figure 5 is a detail of the bimetallic strips under actual operating conditions.

Figure 6 is a side elevation of the bimetallic strips under actual operating conditions.

Figure 7 is a schematic diagram of a discharge lamp circuit using my thermal relay.

Figure 1 shows the thermal relay and the relative position of the parts thereof before it is connected with a source of electrical energy. The filament I is mounted on top of the lead-in wires 2 and 3 and is held in an upright position by th suspending wire I which in turn has its lower end attached to the support wire 5. This filament I may well be large enough to act as a ballast for the lamp or other electrical device to which it is connected in series as well as be the source of heat for distorting the bimetallic strips.

The upper extension of the mounting wire 6 is bent over at an angle of about 90 and has mounted and attached to the top of this bent portion a'bimetallic strip 1 with a tab 8 on the side and bottom of the free end thereof. The bimetallic strip 9 is attached to the mounting wire 6 directly beneath the bimetallic strip I. Th forward free end of this strip 9 is flush with the lead-in wire III.

When a current is caused to flow through the filament I, the heat radiated by the filament will distort the bimetallic strips I and 9. These strips are so spaced in relation to each other and to the filament I that the strip 9 will have been distorted sufficiently to pullaway from its contact with lead-in wire I0 and out from beneath the strip I so that when this strip I has been distorted suificiently to move down into the path through which the strip 9 has travelled, the strip 1 will lock the strip 9 away fromthe lead-in wire ID substantially as shown in Figure 2.

This thermal relay may be used for electric gaseous discharge devices or any other electrical device having a thermal relay, for example, electric irons, thermostats etc. When used with a,

fluorescent lamp, the filaments of the lamp will start to heat up as soon as the lamp and relay is connected to a, source of electricity because the circuit through the relay is then closed since the bimetallic strip 9 and the lead-in wire III are touching each other. As the filament I in the relay heats up, the bimetallic strip 9 will break its contact with the lead-in wire ID. This break is calculated to occur at the time when the ills.- ments of the lamp have been heated sufliciently to carry the discharge across the lamp.

After the lamp starts, th free end of the strip 9 will still continue to be distorted, the strip moving in a clockwise manner away from the lead-in wire Ill. The strip I, attached to the mounting 7 wire 6 will continue to be distorted by the heat from the filament I and the free end thereof with the tab 8 thereon will move down behind the distorted strip 9 thus locking strip 9 away rirlom closing the circuit through the lead-in wire Many difiiculties have been encountered with thermal relays used with fluorescent lamps when a lamp has been shut oil and then suddenly turned on again. The major problem seemed to be to obtain a firm positive contact to close the circuit through the relay. The relay in my invention obviates this difficulty.

While the lamp is running, the elements of the relay assume the position substantially as shown in Figure 2. When the lamp is turned off, and then turned on again quickly, a, firm, positive contact must be obtained in order to have the lamp relight.

In my relay, when the current is shut oil, the

path of strip 9. This being true, it will build up a tension against strip 1 so that when it is released, it will snap back quite vigorously against lead-in wire I0, thus providing the firm, positive contact desired.

Once the contact between the strip 9 and the lead-in wire H) has been established, the filament I will pass current and thereby heat up the bimetallic strips 1 and 9 sufllciently to cause the strip 9 to break away from the lead-in l thus causing the lamp to start.

The tab 8 on the side and bottom of the free end of thebimetallic strip 1 functions in conjunction with the tab II on the face of the free end of the strip 9 which contacts the lead-in wire l0. These tabs serve to aid the strip lin snapping away from its locking position shown in Figure 2.

The lead-in wires and supports which hold the relay assembly extend down into a stem I2. Those wires which are connected electrically extend out from the base 13. The relay assembly may be enclosed in some suitable container for example a glass bulb I l.

The function of the tabs 8 and II may be more clearly understood by a study of Figures and 6. When the two bimetallic strips I and 9 start to cool and strip 1 release strip 9, which has been held away from the lead-in wires I0, these two tabs provide a smooth sliding surface for the release. These tabs thus prevent one strip from catching on the other due to burrs or other rough surface conditions. a

It has been pointed out above that the bimetallic strip 9 does not break away from the lead-in wire ID with the filaments of the lamp have become sufficiently heated to become capable of carrying the discharge across the lamp. This is accomplished by having the strip 9 angularly disposed to create the tension against lead-in wire l0 necessary to provide the delayed action desired.

Figure 7 shows a discharge lamp circuit in which the thermal relay may be used. In this circuit, the filament l in the thermal relay container I4 is connected in series with the lamps i5 and I! as the sole ballast resistance. The bimetallic strip 9 and the lead-in wire i0 which serve as the contacts of the relay are connected between one end of filament ll of lamp i5 and one end of the primary of the transformer 2|. The other end of the primary of the transformer is connected through the filament 20 to the line. This circuit is similar to that shown and described in my copending application Serial No. 362,970, filed October 26, 1940.

What I claim is:

In combination: an electric gaseous discharge device having filamentary electrodes; and a thermal relay for controlling pre-heating of said filamentary electrodes, said relay being enclosed in a sealed container and comprising: a pair of lead-in wires, the inner end of one of said wires being bent substantially at right angles; a bimetallic strip fixed to the top of said wire, of which the top thereof is bent substantially at right angles, and extending toward said other lead-in wire but not in contact therewith; a second bimetallic strip fixed to the same lead-in wire as said first bimetallic strip and extending toward said other lead-in wire and normally in contact therewith; said second strip being in a plane perpendicular to the first strip and normally out of contact therewith; and a ballast, for said discharge device, in the form of a tungsten filament in series with said filamentary electrodes and in such heating relationship with said bimetallic strips as to cause the first of said strips to lock the second strip away from its normally closed position with respect to one 01 said lead wires.

HENRY J. MCCARTHY. 

